Diagnosis of dengue virus infection by detection of specific immunoglobulin M (IgM) and IgA antibodies in serum and saliva

Obesity Is Associated With Increased Pediatric Dengue Virus Infection and Disease: A 9-Year Cohort Study in Managua, Nicaragua

BACKGROUND

Obesity is on the rise globally in adults and children, including in tropical areas where diseases such as dengue have a substantial burden, particularly in children. Obesity impacts risk of severe dengue disease; however, the impact on dengue virus (DENV) infection and dengue cases remains an open question.

METHODS

We used 9 years of data from 5940 children in the Pediatric Dengue Cohort Study in Nicaragua to determine whether pediatric obesity is associated with increased susceptibility to DENV infection and symptomatic presentation. Analysis was performed using generalized estimating equations adjusted for age, sex, and preinfection DENV antibody titers.

RESULTS

From 2011 to 2019, children contributed 26 273 person-years of observation, and we observed an increase in prevalence of overweight (from 12% to 17%) and obesity (from 7% to 13%). There were 1682 DENV infections and 476 dengue cases in the study population. Compared with participants with normal weight, participants with obesity had higher odds of DENV infection (adjusted odds ratio [aOR], 1.21; 95% confidence interval [CI]: 1.03-1.42) and higher odds of dengue in DENV-infected individuals (aOR, 1.59; 95% CI: 1.15-2.19). Children with obesity infected with DENV showed increased odds of presenting fever (aOR, 1.46; 95% CI: 1.05-2.02), headache (aOR, 1.51; 95% CI: 1.07-2.14), and rash (aOR, 2.26; 95% CI: 1.49-3.44) when compared with children with normal weight.

CONCLUSIONS

Our results indicate that obesity is associated with increased susceptibility to DENV infection and dengue cases in children, independent of age, sex, and preinfection DENV antibody titers.

A Cross-Sectional Study on Bedside Abdominal Ultrasound Findings as a Diagnostic and Prognostic Tool in Dengue Fever in Manipal Hospital, Bengaluru, India

Background Dengue fever poses a significant health burden globally, particularly in tropical and subtropical regions. Early diagnosis and effective management are crucial in reducing morbidity and mortality associated with the disease. Bedside abdominal ultrasound has emerged as a promising tool for assessing dengue patients, providing real-time imaging of abdominal organs, and aiding clinical decision-making. Materials and methods This cross-sectional study was conducted in 55 adult emergency departments of Manipal Hospital, Bengaluru, from March 2017 to March 2018. Adult patients presenting with signs and symptoms suggestive of dengue fever were included. Clinical data, laboratory investigations, and bedside abdominal ultrasound findings were systematically recorded and analyzed using appropriate statistical methods. Results Descriptive statistics revealed characteristic clinical measurements and symptom ratings observed in dengue fever patients. Frequency distributions highlighted common symptoms encountered, while statistical analyses demonstrated significant associations between ultrasonic parameters, disease severity, and outcomes. The study found notable correlations between ultrasonic findings and dengue severity levels, emphasizing the potential of bedside ultrasound as a diagnostic and prognostic tool. Conclusion Bedside abdominal ultrasound shows promise as a valuable adjunctive tool in assessing dengue fever patients. The significant associations between ultrasonic parameters and disease severity suggest its utility in risk stratification and guiding clinical management decisions. Incorporating bedside ultrasound into routine practice may improve patient care and outcomes in dengue fever management. Further research is warranted to validate these findings and explore additional bedside ultrasound applications in dengue fever diagnosis and prognosis.

Primary exposure to Zika virus increases risk of symptomatic dengue virus infection with serotypes 2, 3, and 4 but not serotype 1

Infection with any of the four dengue virus serotypes (DENV1-4) can protect against or enhance subsequent dengue depending on pre-existing antibodies and the subsequent infecting serotype. Additionally, primary infection with the related flavivirus Zika virus (ZIKV) has been shown to increase DENV2 disease. Here, we measured how prior DENV and ZIKV immunity influenced risk of disease caused by all four serotypes in a pediatric Nicaraguan cohort. Of 3,412 participants in 2022, 10.6% experienced symptomatic DENV infections caused by DENV1 (n=139), DENV4 (n=133), DENV3 (n=54), DENV2 (n=9), or an undetermined serotype (n=39). Longitudinal clinical and serological data were used to define infection histories, and generalized linear and additive models adjusted for age, sex, time since the last infection, cohort year, and repeat measurements were used to predict disease risk. Compared to flavivirus-naïve participants, primary ZIKV infection increased disease risk of DENV4 (relative risk = 2.62, 95% confidence interval: 1.48-4.63) and DENV3 (2.90, 1.34-6.27) but not DENV1 (1.20, 0.72-1.99). Primary DENV infection or a DENV followed by ZIKV infection also increased DENV4 risk. We re-analyzed 19 years of cohort data and demonstrated that prior flavivirus-immunity and pre-existing antibody titer differentially affected disease risk for incoming serotypes, increasing risk of DENV2 and DENV4, protecting against DENV1, and protecting at high titers but enhancing at low titers against DENV3. We thus find that prior ZIKV infection, like prior DENV infection, increases risk of certain DENV serotypes. Cross-reactivity among flaviviruses should be carefully considered when assessing vaccine safety and efficacy.

Detection of Anti-ZIKV NS1 IgA, IgM, and Combined IgA/IgM and Identification of IL-4 and IL-10 as Potential Biomarkers for Early ZIKV and DENV Infections in Hyperendemic Regions, Thailand

The frequency of Zika virus (ZIKV)-specific IgA and IgM and the cytokine expression profile of ZIKV-infected patients in hyperendemic areas remain unclear. This study investigated the rates of ZIKV non-structural protein 1 (NS1)-specific IgA and IgM and evaluated serum cytokine levels of ZIKV and Dengue virus (DENV) cases in Thailand to identify potential diagnostic biomarkers, elucidate the immunity against ZIKV and DENV, and investigate the association between cytokine levels and ZIKV symptoms. Low rates of positivity for ZIKV NS1-specific IgA and IgM were detected in our study. ZIKV NS1 IgA/M (11%, 11/101) in combination was more frequently detected than ZIKV NS1 IgM (2%, 2/101) or ZIKV NS1 IgA (4%, 4/96) alone, especially in acute ZIKV cases with previous DENV exposure (14%, 10/72). Cytokine analysis showed that both ZIKV and DENV infections induced polyfunctional immunity, and the latter triggered more prolonged responses. The existence of significant differences in IL-4 and IL-10 levels between acute ZIKV and acute DENV cases suggested that IL-4 (p = 0.0176) and IL-10 (p = 0.0003) may represent biomarkers for acute ZIKV and acute DENV infections, respectively. Analysis of the association between increased cytokine levels and ZIKV symptoms indicated that CXCL10 (p = 0.0029) was associated with exanthema, while IL-5 (p = 0.0496) was linked to headache. The detection of ZIKV NS1 IgA and IgM in combination may enhance the diagnosis of early ZIKV infection, particularly when levels of IgM or IgA alone are low or undetectable. IL-4 and IL-10 may serve as targets for the development of diagnostic tools to detect ZIKV and DENV infections early, respectively, in flavivirus-endemic regions.

Diagnostic performance of anti-Zika virus IgM, IgAM and IgG ELISAs during co-circulation of Zika, dengue, and chikungunya viruses in Brazil and Venezuela

Background

Serological diagnosis of Zika virus (ZIKV) infection is challenging because of the antibody cross-reactivity among flaviviruses. At the same time, the role of Nucleic Acid Testing (NAT) is limited by the low proportion of symptomatic infections and the low average viral load. Here, we compared the diagnostic performance of commercially available IgM, IgAM, and IgG ELISAs in sequential samples during the ZIKV and chikungunya (CHIKV) epidemics and co-circulation of dengue virus (DENV) in Brazil and Venezuela.

Methodology/Principal findings

Acute (day of illness 1–5) and follow-up (day of illness ≥ 6) blood samples were collected from nine hundred and seven symptomatic patients enrolled in a prospective multicenter study between June 2012 and August 2016. Acute samples were tested by RT-PCR for ZIKV, DENV, and CHIKV. Acute and follow-up samples were tested for IgM, IgAM, and IgG antibodies to ZIKV using commercially available ELISAs. Among follow-up samples with a RT-PCR confirmed ZIKV infection, anti-ZIKV IgAM sensitivity was 93.5% (43/46), while IgM and IgG exhibited sensitivities of 30.3% (10/33) and 72% (18/25), respectively. An additional 24% (26/109) of ZIKV infections were detected via IgAM seroconversion in ZIKV/DENV/CHIKV RT-PCR negative patients. The specificity of anti-ZIKV IgM was estimated at 93% and that of IgAM at 85%.

Conclusions/Significance

Our findings exemplify the challenges of the assessment of test performance for ZIKV serological tests in the real-world setting, during co-circulation of DENV, ZIKV, and CHIKV. However, we can also demonstrate that the IgAM immunoassay exhibits superior sensitivity to detect ZIKV RT-PCR confirmed infections compared to IgG and IgM immunoassays. The IgAM assay also proves to be promising for detection of anti-ZIKV seroconversions in sequential samples, both in ZIKV PCR-positive as well as PCR-negative patients, making this a candidate assay for serological monitoring of pregnant women in future ZIKV outbreaks.

Zika virus (ZIKV) is transmitted through the bite of infected Aedes mosquitos but can also be transmitted sexually or vertically from mother-to-child. The same mosquitoes transmit dengue virus (DENV) and chikungunya virus (CHIKV), which cause similar clinical syndromes. The ZIKV epidemics in the Pacific and the Americas that occurred between 2015 and 2017 were linked to congenital abnormalities, most prominently microcephaly, in newborns. Because most infections are asymptomatic, diagnosis via indirect serological assays is an important strategy. On the other hand, many serological assays are affected by cross-reactivity resulting from prior infections by closely related viruses, such as DENV. This study evaluated three commercially available and widely used immunoassays that detect IgG, IgM or IgA and M (IgAM) antibodies to ZIKV. Our results suggest that the IgAM test performs best by detecting around 90% of RT-PCR confirmed infections. We also detected additional infections that were not detected by RT-PCR. The strength of this study is that it was carried out in two different countries of the American region where several arboviruses are endemic and that sequential blood samples from individual patients were available to evaluate the performance of the tests over time.

Identification of Dengue Virus Serotype 3 Specific Antigenic Sites Targeted by Neutralizing Human Antibodies

The rational design of dengue virus (DENV) vaccines requires a detailed understanding of the molecular basis for antibody-mediated immunity. The durably protective antibody response to DENV after primary infection is serotype specific. However, there is an incomplete understanding of the antigenic determinants for DENV type-specific (TS) antibodies, especially for DENV serotype 3, which has only one well-studied, strongly neutralizing human monoclonal antibody (mAb). Here, we investigated the human B cell response in children after natural DENV infection in the endemic area of Nicaragua and isolated 15 DENV3 TS mAbs recognizing the envelope (E) glycoprotein. Functional epitope mapping of these mAbs and small animal prophylaxis studies revealed a complex landscape with protective epitopes clustering in at least 6-7 antigenic sites. Potently neutralizing TS mAbs recognized sites principally in E glycoprotein domains I and II, and patterns suggest frequent recognition of quaternary structures on the surface of viral particles.

Utility of entomological indices for predicting transmission of dengue virus: secondary analysis of data from the Camino Verde trial in Mexico and Nicaragua

Dengue vector entomological indices are widely used to monitor vector density and disease control activities. But the value of these indices as predictors of dengue infection is not established. We used data from the impact assessment of a trial of community mobilization for dengue prevention (Camino Verde) to examine the associations between vector indices and evidence of dengue infection and their value for predicting dengue infection levels. In 150 clusters in Mexico and Nicaragua, two entomological surveys, three months apart, allowed calculation of the mean Container Index, Breteau index, Pupae per Household Index, and Pupae per Container Index across the two surveys. We measured recent dengue virus infection in children, indicated by a doubling of dengue antibodies in paired saliva samples over the three-month period. We examined the associations between each of the vector indices and evidence of dengue infection at household level and at cluster level, accounting for trial intervention status. To examine the predictive value for dengue infection, we constructed receiver operating characteristic (ROC) curves at household and cluster level, considering the four vector indices as continuous variables, and calculated the positive and negative likelihood ratios for different levels of the indices. None of the vector indices was associated with recent dengue infection at household level. The Breteau Index was associated with recent infection at cluster level (Odds ratio 1.36, 95% confidence interval 1.14–1.61). The ROC curve confirmed the weak predictive value for dengue infection of the Breteau Index at cluster level. Other indices showed no predictive value. Conventional vector indices were not useful in predicting dengue infection in Mexico and Nicaragua. The findings are compatible with the idea of sources of infection outside the household which were tackled by community action in the Camino Verde trial.

Vector control is the basis of preventing dengue virus infection. Measurement of dengue vector indices is widely used to monitor dengue control activities, but their utility as predictors of dengue infection is not clear. We used data about vector indices and evidence of recent dengue virus infection from a trial of community mobilization for dengue prevention in Mexico and Nicaragua (Camino Verde), to examine how four standard vector indices could predict dengue infection. Only the Breteau index was associated with evidence of dengue infection, and that only at cluster level. Receiver operating characteristic (ROC) curves confirmed the Breteau Index was only a weak predictor of infection at cluster level; none of the other indices had predictive value. These findings indicate that the four entomological indices studied were not useful predictors of dengue infection. The results are compatible with the idea of sources of infection outside the household which were tackled by community action in the Camino Verde trial.

Saliva is a non-negligible factor in the spread of COVID-19

SARS‐CoV‐2, a novel emerging coronavirus, has caused severe disease (COVID‐19), and rapidly spread worldwide since the beginning of 2020. SARS‐CoV‐2 mainly spreads by coughing, sneezing, droplet inhalation, and contact. SARS‐CoV‐2 has been detected in saliva samples, making saliva a potential transmission route for COVID‐19. The participants in dental practice confront a particular risk of SARS‐CoV‐2 infection due to close contact with the patients and potential exposure to saliva‐contaminated droplets and aerosols generated during dental procedures. In addition, saliva‐contaminated surfaces could lead to potential cross‐infection. Hence, the control of saliva‐related transmission in the dental clinic is critical, particularly in the epidemic period of COVID‐19. Based on our experience of the COVID‐19 epidemic, some protective measures that can help reduce the risk of saliva‐related transmission are suggested, in order to avoid the potential spread of SARS‐CoV‐2 among patients, visitors, and dental practitioners.

Transcriptional and clonal characterization of B cell plasmablast diversity following primary and secondary natural DENV infection

Antibody-mediated humoral immunity is thought to play a central role in mediating the immunopathogenesis of acute DENV infection, but limited data are available on the diversity, specificity, and functionality of the antibody response at the molecular level elicited by primary or secondary DENV infection. In order to close this functional gap in our understanding of DENV-specific humoral immunity, we utilized high-throughput single cell RNA sequencing to investigate B cells circulating in both primary and secondary natural DENV infections. We captured full-length paired immunoglobulin receptor sequence data from 9,027 B cells from a total of 6 subjects, including 2,717 plasmablasts. In addition to IgG and IgM class-switched cells, we unexpectedly found a high proportion of the DENV-elicited plasmablasts expressing IgA, principally in individuals with primary DENV infections. These IgA class-switched cells were extensively hypermutated even in individuals with a serologically confirmed primary DENV infection. Utilizing a combination of conventional biochemical assays and high-throughput shotgun mutagenesis, we determined that DENV-reactive IgA class-switched antibodies represent a significant fraction of DENV-reactive Igs generated in response to DENV infection, and that they exhibit a comparable epitope specificity to DENV-reactive IgG antibodies. These results provide insight into the molecular-level diversity of DENV-elicited humoral immunity and identify a heretofore unappreciated IgA plasmablast response to DENV infection.

A need to raise the bar - A systematic review of temporal trends in diagnostics for Japanese encephalitis virus infection, and perspectives for future research

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Japanese encephalitis virus (JEV) remains a leading cause of neurological infection in Asia.

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A systematic review identified 20,212 published human cases of laboratory-confirmed JEV infections from 205 studies.

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15,167 (75%) of cases were confirmed with the lowest confidence diagnostic test, i.e., level 3 or 4, or level 4.

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Only 109 (53%) of the studies reported contemporaneous testing for dengue-specific antibodies.

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A fundamental pre-requisite for the control of JE is lacking — that of a simple and specific diagnostic procedure that can be adapted for point-of-care tests and readily used throughout JE endemic regions of the world.

Objective

Japanese encephalitis virus infection (JE) remains a leading cause of neurological disease in Asia, mainly involving individuals living in remote areas with limited access to treatment centers and diagnostic facilities. Laboratory confirmation is fundamental for the justification and implementation of vaccination programs. We reviewed the literature on historical developments and current diagnostic capability worldwide, to identify knowledge gaps and instill urgency to address them.

Methods

Searches were performed in Web of Science and PubMed using the term 'Japanese encephalitis' up to 13th October 2019. Studies reporting laboratory-confirmed symptomatic JE cases in humans were included, and data on details of diagnostic tests were extracted. A JE case was classified according to confirmatory levels (Fischer et al., 2008; Campbell et al., 2011; Pearce et al., 2018; Heffelfinger et al., 2017), where level 1 represented the highest level of confidence.

Findings

20,212 published JE cases were identified from 205 studies. 15,167 (75%) of these positive cases were confirmed with the lowest-confidence diagnostic tests (level 3 or 4, or level 4). Only 109 (53%) of the studies reported contemporaneous testing for dengue-specific antibodies.

Conclusion

A fundamental pre-requisite for the control of JEV is lacking — that of a simple and specific diagnostic procedure that can be adapted for point-of-care tests and readily used throughout JE-endemic regions of the world.

A novel method to diagnose the infection of enterovirus A71 in children by detecting IgA from saliva

Enterovirus A71 (EV-A71) is one of the main pathogens causing hand, foot, and mouth disease, and often causes diseases of the central nervous system. Early diagnosis is important to prevent EV-A71 outbreaks. The detection of serum immunoglobulin M (IgM) is widely used for the early diagnosis of EV-A71 in clinics, especially in rural areas. However, this technique requires the extraction of blood from children who have thin blood vessels and who might fear the use of needles. Therefore, difficulties in the detection process are often encountered. This study developed a noninvasive method to detect EV-A71-specific immunoglobulin A (IgA) in saliva for the diagnosis of EV-A71 infection. The sensitivity and specificity of IgA detection did not differ significantly compared with IgM detection. IgA antibodies were present in saliva for a relatively shorter period than IgM antibodies were present in serum. The sensitivity of IgA detection was higher than that of IgM detection for secondary EV-A71 infections. These results suggest that the detection of EV-A71-specific IgA in the saliva allows the effective early diagnosis of EV-A71 and may be suitable for detecting EV-A71 infections in children.

Tracking the polyclonal neutralizing antibody response to a dengue virus serotype 1 type-specific epitope across two populations in Asia and the Americas

The four dengue virus serotypes (DENV1-4) cause major public health problems worldwide. Highly neutralizing type-specific human monoclonal antibodies (hmAbs) target conformation-dependent epitopes on the DENV envelope protein, including 1F4, a DENV1 type-specific hmAb. Using a recombinant DENV2 virus displaying the DENV1 1F4 epitope (rDENV2/1), we measured the proportion and kinetics of DENV1 neutralizing antibodies targeting the 1F4 epitope in individuals living in Asia and the Americas where different DENV1 genotypes were circulating. Samples from 20 individuals were analyzed 3 and 18 months post-primary DENV1 infection, alongside samples from 4 individuals collected annually for four years post-primary DENV1 infection, from two studies in Nicaragua. We also analyzed convalescent post-primary DENV1 plasma samples from Sri Lankan individuals. We found that neutralizing antibodies recognizing the 1F4 epitope vary in prevalence across both populations and were detected from 20 days to four years post-infection. Additionally, both populations displayed substantial variability, with a range of high to low proportions of DENV1 type-specific neutralizing antibodies recognizing the 1F4 epitope seen across individuals. Thus, the 1F4 epitope is a major but not exclusive target of type-specific neutralizing antibodies post-primary infection with different DENV1 genotypes in Asia and Latin America, and additional epitopes likely contribute to type-specific neutralization of DENV1.

The Application and Interpretation of IgG Avidity and IgA ELISA Tests to Characterize Zika Virus Infections

In the absence of viremia, the diagnostics of Zika virus (ZIKV) infections must rely on serological techniques. In order to improve the serological diagnosis of ZIKV, ZIKV-IgA and ZIKV-IgG avidity assays were evaluated. Forty patients returning from ZIKV endemic areas, with confirmed or suspected ZIKV infections were studied. Samples were classified as early acute, acute and late acute according to the number of days post illness onset. Low avidity IgG was only detected at acute and late acute stages and IgA mostly at the early acute and acute stages. The date of sampling provides useful information and can help to choose the best technique to use at a determined moment in time and to interpret low avidity IgG and IgA results, improving the serological diagnosis of ZIKV.

Find the right sample: A study on the versatility of saliva and urine samples for the diagnosis of emerging viruses

BACKGROUND

The emergence of different viral infections during the last decades like dengue, West Nile, SARS, chikungunya, MERS-CoV, Ebola, Zika and Yellow Fever raised some questions on quickness and reliability of laboratory diagnostic tests for verification of suspected cases. Since sampling of blood requires medically trained personal and comprises some risks for the patient as well as for the health care personal, the sampling by non-invasive methods (e.g. saliva and/ or urine) might be a very valuable alternative for investigating a diseased patient.

MAIN BODY

To analyse the usefulness of alternative non-invasive samples for the diagnosis of emerging infectious viral diseases, a literature search was performed on PubMed for alternative sampling for these viral infections. In total, 711 papers of potential relevance were found, of which we have included 128 in this review.

CONCLUSIONS

Considering the experience using non-invasive sampling for the diagnostic of emerging viral diseases, it seems important to perform an investigation using alternative samples for routine diagnostics. Moreover, during an outbreak situation, evaluation of appropriate sampling and further processing for laboratory analysis on various diagnostic platforms are very crucial. This will help to achieve optimal diagnostic results for a good and reliable case identification.

Accuracy of immunoglobulin M and immunoglobulin A of saliva in early diagnosis of dengue: Systematic Review and Meta-analysis

The objective of the study was to conduct a systematic review to synthesize the current evidence on the accuracy of IgM and IgA to early diagnosis the dengue virus. The review protocol was registered at PROSPERO (CRD 42015024808). We searched for studies in the following electronic database from 1990 to January 2018. The search identified 3507 studies. Five studies were included for quantitative analysis. Three studies included evaluations of salivary IgM provided a sensitivity of 86% and specificity of 93%. Two studies included evaluating of IgA salivary showed a combined sensitivity of 69% and a combined specificity of 98%. Despite the results found and the low methodological quality of the studies included in the meta-analysis it is still soon to claim that IgA is better than IgM to diagnosis Dengue.

Zika virus infection in Nicaraguan households

Zika virus (ZIKV) infection recently caused major epidemics in the Americas and is linked to congenital birth defects and Guillain-Barré Syndrome. A pilot study of ZIKV infection in Nicaraguan households was conducted from August 31 to October 21, 2016, in Managua, Nicaragua. We enrolled 33 laboratory-confirmed Zika index cases and their household members (109 contacts) and followed them on days 3–4, 6–7, 9–10, and 21, collecting serum/plasma, urine, and saliva specimens along with clinical, demographic, and socio-economic status information. Collected samples were processed by rRT-PCR to determine viral load (VL) and duration of detectable ZIKV RNA in human bodily fluids. At enrollment, 11 (10%) contacts were ZIKV rRT-PCR-positive and 23 (21%) were positive by IgM antibodies; 3 incident cases were detected during the study period. Twenty of 33 (61%) index households had contacts with ZIKV infection, with an average of 1.9 (range 1–6) positive contacts per household, and in 60% of these households, ≥50% of the members were positive for ZIKV infection. Analysis of clinical information allowed us to estimate the symptomatic to asymptomatic (S:A) ratio of 14:23 (1:1.6) among the contacts, finding 62% of the infections to be asymptomatic. The maximum number of days during which ZIKV RNA was detected was 7 days post-symptom onset in saliva and serum/plasma and 22 days in urine. Overall, VL levels in serum/plasma, saliva, and urine specimens were comparable, with means of 5.6, 5.3 and 4.5 log₁₀ copies/ml respectively, with serum attaining the highest VL peak at 8.1 log₁₀ copies/ml. Detecting ZIKV RNA in saliva over a similar time-period and level as in serum/plasma indicates that saliva could potentially serve as a more accessible diagnostic sample. Finding the majority of infections to be asymptomatic emphasizes the importance of silent ZIKV transmission and helps inform public health interventions in the region and globally.

Zika virus (ZIKV) infection has become a major concern due to its association with congenital birth defects and Guillain-Barré Syndrome. We enrolled 33 laboratory-confirmed Zika cases (index cases) and their household members (109 contacts) in Managua, Nicaragua, and followed them for three weeks, collecting serum/plasma, urine and saliva specimens along with clinical, demographic, and socio-economic status information. We found that 61% of the index households had contacts with ZIKV infection, with an average of 1.9 (range 1–6) positive contacts per household, and in 60% of these households, ≥50% of the members were ZIKV-positive. Analysis of clinical information allowed estimating the symptomatic to asymptomatic (S:A) ratio of 14:23 (1:1.6) among the contacts. Finding 62% of the infections to be asymptomatic emphasizes the importance of silent transmission. Evaluating the maximum number of days during which ZIKV RNA was detectable showed that ZIKV was found up to 7 days post-symptom onset in serum/plasma and saliva and 22 days post-symptom onset in urine. Finding ZIKV RNA in saliva over a similar time period and concentration as serum/plasma indicates that saliva could potentially serve as a more accessible diagnostic sample. Overall, these data increase our understanding of ZIKV transmission and help inform public health interventions in the region and globally.

Development of antibody biomarkers of long term and recent dengue virus infections

Dengue virus (DENV) infections elicit antibody responses to the non-structural protein 1 (NS1) that are associated with protection against disease. However, the antibody isotypes and subclasses involved, and their kinetics have not been extensively studied. We characterized the antibody responses to DENV NS1 by enzyme-linked immunosorbent assay (ELISA) in a longitudinal cohort of 266 confirmed dengue cases in Recife, Northeast Brazil. Samples were collected during the febrile phase and up to over 3 years after onset of symptoms. The antibodies investigated [IgA, IgM, total IgG (all subclasses measured together) and each subclass (IgG2, IgG3 and IgG4) measured separately] had distinct kinetic profiles following primary or secondary DENV infections. Of interest, most of these antibodies were consistently detected greater than 6 months after onset of symptoms, except for IgG3. Anti-dengue NS1-specific IgG was consistently detected from the acute phase to beyond 3 years after symptom onset. In contrast, anti-dengue NS1-specific IgG3 was detected within the first week, peaked at week 2-3, and disappeared within 4-6 months after onset of symptoms. The mean duration of the IgG3 positive signal was 149 days (ranging from 126 to 172 days). In conclusion, anti-dengue NS1-specific IgG and IgG3 are potential biomarkers of long-term and recent (less than 6 months) DENV infections, respectively.

Comparison of Four Serological Methods and Two Reverse Transcription-PCR Assays for Diagnosis and Surveillance of Zika Virus Infection

Zika virus (ZIKV) is a mosquito-borne flavivirus that is responsible for recent explosive epidemics in the Americas. Notably, ZIKV infection during pregnancy has been found to cause congenital birth defects, including microcephaly, and ZIKV has been associated with Guillain-Barré syndrome in adults. Diagnosis and surveillance of Zika in the Americas have been challenging due to similar clinical manifestations and extensive antibody cross-reactivity with endemic flaviviral diseases, such as dengue. We evaluated four serological and two reverse transcription-PCR (RT-PCR) methods in acute-phase (mean day, 1.8), early-convalescent-phase (mean day, 16.7), and late-convalescent-phase (mean, ~7 months) samples from the same individuals in a long-term pediatric cohort study in Nicaragua. Well-characterized samples from 301 cases of Zika, dengue, or non-Zika, nondengue febrile illnesses were tested. Compared to a composite reference, an in-house IgM antibody capture enzyme-linked immunosorbent assay (MAC-ELISA) and the NIAID-Biodefense and Emerging Infections (BEI) MAC-ELISA measuring IgM yielded sensitivities of 94.5% and 70.1% and specificities of 85.6% and 82.8%, respectively. The NS1 blockade-of-binding ELISA measuring anti-ZIKV NS1 antibody levels yielded sensitivities of 85.0% and 96.5% and specificities of 91.4% and 92.6% at early and late convalescence, respectively. An inhibition ELISA detecting total anti-ZIKV antibodies had sensitivity and specificity values of 68.3% and 58.3% for diagnosis and 94.0% and 98.6% for measuring annual infection incidence. Finally, the ZCD and Trioplex real-time RT-PCR assays detecting Zika, chikungunya, and dengue viruses both yielded a sensitivity of 96.1% and specificity of 100%. Together, these assays resolve the urgent need for diagnostic and surveillance tools for countries affected by Zika virus infections.

First detection of dengue virus in the saliva of immunocompetent murine model

The lack of an experimental animal model for the study of dengue pathogenesis is a limiting factor for the development of vaccines and drugs. In previous studies, our group demonstrated the susceptibility of BALB/c mice to infection by dengue virus (DENV) 1 and 2, and the virus was successfully isolated in several organs. In this study, BALB/c mice were experimentally infected intravenously with DENV-4, and samples of their saliva were collected. Viral RNA extracted from the saliva samples was subjected to qRT-PCR, with a detection limit of 0.002 PFU/mL. The presence of DENV-4 viral RNA was detected in the saliva of two mice, presenting viral titers of 109 RNA/mL. The detection of DENV RNA via saliva sampling is not a common practice in dengue diagnosis, due to the lower detection rates in human patients. However, the results observed in this study seem to indicate that, as in humans, detection rates of DENV RNA in mouse saliva are also low, correlating the infection in both cases. This study reports the first DENV detection in the saliva of BALB/c immunocompetent mice experimentally infected with non-neuroadapted DENV-4.

Development of in-house serological methods for diagnosis and surveillance of chikungunya

OBJECTIVE

To develop and evaluate serological methods for chikungunya diagnosis and research in Nicaragua.

METHODS

Two IgM ELISA capture systems (MAC-ELISA) for diagnosis of acute chikungunya virus (CHIKV) infections, and two Inhibition ELISA Methods (IEM) to measure total antibodies against CHIKV were developed using monoclonal antibodies (mAbs) and hyperimmune serum at the National Virology Laboratory of Nicaragua in 2014-2015. The sensitivity, specificity, predictive values, and agreement of the MAC-ELISAs were obtained by comparing the results of 198 samples (116 positive; 82 negative) with the Centers for Disease Control and Prevention's IgM ELISA (Atlanta, Georgia, United States; CDC-MAC-ELISA). For clinical evaluation of the four serological techniques, 260 paired acute and convalescent phase serum samples of suspected chikungunya cases were used.

RESULTS

All four assays were standardized by determining the optimal concentrations of the different reagents. Processing times were substantially reduced compared to the CDC-MAC-ELISA. For the MAC-ELISA systems, a sensitivity of 96.6% and 97.4%, and a specificity of 98.8% and 91.5% were obtained using mAb and hyperimmune serum, respectively, compared with the CDC method. Clinical evaluation of the four serological techniques versus the CDC real-time RT-PCR assay resulted in a sensitivity of 95.7% and a specificity of 88.8%-95.9%.

CONCLUSION

Two MAC-ELISA and two IEM systems were standardized, demonstrating very good quality for chikungunya diagnosis and research demands. This will achieve more efficient epidemiological surveillance in Nicaragua, the first country in Central America to produce its own reagents for serological diagnosis of CHIKV. The methods evaluated here can be applied in other countries and will contribute to sustainable diagnostic systems to combat the disease.

PCA-MLP SVM distinction of salivary Raman spectra of dengue fever infection

Dengue fever (DF) is a disease of major concern caused by flavivirus infection. Delayed diagnosis leads to severe stages, which could be deadly. Of recent, non-structural protein (NS1) has been acknowledged as a biomarker, alternative to immunoglobulins for early detection of dengue in blood. Further, non-invasive detection of NS1 in saliva makes the approach more appealing. However, since its concentration in saliva is less than blood, a sensitive and specific technique, Surface Enhanced Raman Spectroscopy (SERS), is employed. Our work here intends to define an optimal PCA-SVM (Principal Component Analysis-Support Vector Machine) with Multilayer Layer Perceptron (MLP) kernel model to distinct between positive and negative NS1 infected samples from salivary SERS spectra, which, to the best of our knowledge, has never been explored. Salivary samples of DF positive and negative subjects were collected, pre-processed and analyzed. PCA and SVM classifier were then used to differentiate the SERS analyzed spectra. Since performance of the model depends on the PCA criterion and MLP parameters, both are examined in tandem. Its performance is also compared to our previous works on simulated NS1 salivary samples. It is found that the best PCA-SVM (MLP) model can be defined by 95 PCs from CPV criterion with P1 and P2 values of 0.01 and -0.2 respectively. A classification performance of [76.88%, 85.92%, 67.83%] is achieved.

Identification of specific antibodies against the Ag85C-MPT51-HspX fusion protein (CMX) for serological screening of tuberculosis in endemic area

OBJECTIVES

Development of new tools for rapid and accurate diagnosis of tuberculosis (TB) is considered a strategy for controlling the disease. The recombinant CMX fusion protein is composed of immunodominant epitopes of the Ag85C (Rv0129c), MPT51 (Rv3803c) and the entire HspX (Rv2031c) proteins from Mycobacterium tuberculosis H37Rv (Mtb). The aim of this study was to evaluate the applicability of a test using the CMX protein in individuals suspected of TB.

METHODS

Indirect ELISA was used to measure serum anti-CMX IgM and IgG in individuals with pulmonary TB.

RESULTS

Patients with pulmonary TB had higher titers of IgM (OD = 0.502 ± 0.281) than healthy controls (OD = 0.200 ± 0.125). The cutoff for IgM-ELISA was determined using ROC curve analyzes (AUC = 0.868) with a sensitivity of 80.1% and a specificity of 78.2%. Patients with pulmonary TB also had higher titers of IgG (OD = 0.525 ± 0.391) than healthy controls (OD = 0.215 ± 0.077). The cutoff for IgG-ELISA was determined using ROC curve analyzes (AUC = 0.864) with a sensitivity of 81.7% and a specificity of 74.7%.

CONCLUSION

The results suggest that the recombinant protein CMX can be used in a serological test to complement the screening of individuals suspected of having active pulmonary TB.

Development of in-house serological methods for diagnosis and surveillance of chikungunya

Objective.

To develop and evaluate serological methods for chikungunya diagnosis and research in Nicaragua.

Methods.

Two IgM ELISA capture systems (MAC-ELISA) for diagnosis of acute chikungunya virus (CHIKV) infections, and two Inhibition ELISA Methods (IEM) to measure total antibodies against CHIKV were developed using monoclonal antibodies (mAbs) and hyperimmune serum at the National Virology Laboratory of Nicaragua in 2014–2015. The sensitivity, specificity, predictive values, and agreement of the MAC-ELISAs were obtained by comparing the results of 198 samples (116 positive; 82 negative) with the Centers for Disease Control and Prevention’s IgM ELISA (Atlanta, Georgia, United States; CDC-MAC-ELISA). For clinical evaluation of the four serological techniques, 260 paired acute and convalescent phase serum samples of suspected chikungunya cases were used.

Results.

All four assays were standardized by determining the optimal concentrations of the different reagents. Processing times were substantially reduced compared to the CDC-MAC-ELISA. For the MAC-ELISA systems, a sensitivity of 96.6% and 97.4%, and a specificity of 98.8% and 91.5% were obtained using mAb and hyperimmune serum, respectively, compared with the CDC method. Clinical evaluation of the four serological techniques versus the CDC real-time RT-PCR assay resulted in a sensitivity of 95.7% and a specificity of 88.8%–95.9%.

Conclusion.

Two MAC-ELISA and two IEM systems were standardized, demonstrating very good quality for chikungunya diagnosis and research demands. This will achieve more efficient epidemiological surveillance in Nicaragua, the first country in Central America to produce its own reagents for serological diagnosis of CHIKV. The methods evaluated here can be applied in other countries and will contribute to sustainable diagnostic systems to combat the disease.

Quantitative Lateral Flow Assays for Salivary Biomarker Assessment: A Review

Saliva is an emerging biofluid with a significant number of applications in use across research and clinical settings. The present paper explores the reasons why saliva has grown in popularity in recent years, balancing both the potential strengths and weaknesses of this biofluid. Focusing on reasons why saliva is different from other common biological fluids such as blood, urine, or tears, we review how saliva is easily obtained, with minimal risk to the donor, and reduced costs for collection, transportation, and analysis. We then move on to a brief review of the history and progress in rapid salivary testing, again reviewing the strengths and weaknesses of rapid immunoassays (e.g., lateral flow immunoassay) compared to more traditional immunoassays. We consider the potential for saliva as an alternative biofluid in a setting where rapid results are important. We focus the review on salivary tests for small molecule biomarkers using cortisol as an example. Such salivary tests can be applied readily in a variety of settings and for specific measurement purposes, providing researchers and clinicians with opportunities to assess biomarkers in real time with lower transportation, collection, and analysis costs, faster turnaround time, and minimal training requirements. We conclude with a note of cautious optimism that the field will soon gain the ability to collect and analyze salivary specimens at any location and return viable results within minutes.

Dengue occurrence relations and serology: cross-sectional analysis of results from the Guerrero State, Mexico, baseline for a cluster-randomised controlled trial of community mobilisation for dengue prevention

Background

The Mexican arm of the Camino Verde trial of community mobilisation for dengue prevention covered three coastal regions of Guerrero state: Acapulco, Costa Grande and Costa Chica. A baseline cross-sectional survey provided data for community mobilisation and for adapting the intervention design to concrete conditions in the intervention areas.

Methods

Trained field teams constructed community profiles in randomly selected clusters, based on observation and key informant interviews. In each household they carried out an entomological inspection of water containers, collected information on socio-demographic variables and cases of dengue illness among household members in the last year, and gathered paired saliva samples from children aged 3–9 years, which were subjected to ELISA testing to detect recent dengue infection. We examined associations with dengue illness and recent dengue infection in bivariate and then multivariate analysis.

Results

In 70/90 clusters, key informants were unable to identify any organized community groups. Some 1.9% (1029/55,723) of the household population reported dengue illness in the past year, with a higher rate in Acapulco region. Among children 3–9 years old, 6.1% (392/6382) had serological evidence of recent dengue infection. In all three regions, household use of anti-mosquito products, household heads working, and households having less than 5 members were associated with self-reported dengue illness. In Acapulco region, people aged less than 25 years, those with a more educated household head and those from urban sites were also more likely to report dengue illness, while in Costa Chica and Costa Grande, females were more likely to report dengue illness. Among children aged 3–9 years, those aged 3–4 years and those living in Acapulco were more likely to have evidence of recent dengue infection.

Conclusions

The evidence from the baseline survey provided important support for the design and implementation of the trial intervention. The weakness of community leadership and the relatively low rates of self-reported dengue illness were challenges that the Mexican intervention team had to overcome. The higher dengue illness occurrence among women in Costa Grande and Costa Chica may help explain why women participated more than men in activities during the Camino Verde trial.

Antibody Epitopes Identified in Critical Regions of Dengue Virus Nonstructural 1 Protein in Mouse Vaccination and Natural Human Infections

Dengue is a global public health problem and is caused by four dengue virus (DENV) serotypes (DENV1-4). A major challenge in dengue vaccine development is that cross-reactive anti-DENV Abs can be protective or potentially increase disease via Ab-dependent enhancement. DENV nonstructural protein 1 (NS1) has long been considered a vaccine candidate as it avoids Ab-dependent enhancement. In this study, we evaluated survival to challenge in a lethal DENV vascular leak model in mice immunized with NS1 combined with aluminum and magnesium hydroxide, monophosphoryl lipid A + AddaVax, or Sigma adjuvant system+CpG DNA, compared with mice infected with a sublethal dose of DENV2 and mice immunized with OVA (negative control). We characterized Ab responses to DENV1, 2, and 3 NS1 using an Ag microarray tiled with 20-mer peptides overlapping by 15 aa and identified five regions of DENV NS1 with significant levels of Ab reactivity in the NS1 + monophosphoryl lipid A + AddaVax group. Additionally, we profiled the Ab responses to NS1 of humans naturally infected with DENV2 or DENV3 in serum samples from Nicaragua collected at acute, convalescent, and 12-mo timepoints. One region in the wing domain of NS1 was immunodominant in both mouse vaccination and human infection studies, and two regions were identified only in NS1-immunized mice; thus, vaccination can generate Abs to regions that are not targeted in natural infection and could provide additional protection against lethal DENV infection. Overall, we identified a small number of immunodominant regions, which were in functionally important locations on the DENV NS1 protein and are potential correlates of protection.

Dengue Specific Immunoglobulin A Antibody is Present in Urine and Associated with Disease Severity

The kinetics of dengue virus (DENV)-specific IgA antibody in urine and the potential correlation with disease severity remain elusive. In this study, 262 serial urine samples from 78 laboratory-confirmed patients were assayed by a commercial immunoglobulin A (IgA) kit against DENV. All cases were classified into dengue fever (DF) and severe dengue (SD) according to the 2009 WHO/TDR guideline. The total positive rate of IgA in urine was 59%. DENV-specific IgA was detected in urine from day 2 to day 13 after the onset of illness in DF patients; While for SD patients, anti-DENV IgA could be detected till day 14. The positive rate of IgA in patients with secondary infection was higher than that in patients with primary infection. Importantly, during 4-7 days after the onset of illness, the IgA positive rate of SD patients was significantly higher than that of DF patients. Especially, the intensity of IgA signal in SD patients was obviously stronger than that in DF patient at the recovery stage. Overall, our results suggested that the existence of DENV-specific IgA antibodies in urine might be a warning sign for the severity of disease and its measurement might provide valuable guidance for proper patient management.

Evaluation of the performances of six commercial kits designed for dengue NS1 and anti-dengue IgM, IgG and IgA detection in urine and saliva clinical specimens

Background

Rapid diagnostic tests (RDTs) have been commercialized in order to help physicians in dengue diagnosis. Until recently, only blood samples were used for those tests but it has been shown in several studies that urine and saliva can also be employed for dengue diagnosis. RDTs for the detection of NS1 antigen and anti-dengue IgG, IgM and IgA in urine and saliva specimens have thus been developed by Standard Diagnostics. The aim of this study was to evaluate the performances these new commercial assays.

Methods

Two panels of clinical specimens were used: one for the evaluation of the NS1-detection devices and the second for the evaluation of the antibody-detection kits. Each panel consisted of urine and saliva specimens collected sequentially from 86 patients with a confirmed dengue infection. A total of 291 saliva and 440 urine samples were included in the NS1-evaluation panel and 530 saliva and 528 urine specimens constituted the antibody-evaluation panel. All samples were tested in parallel by in-house ELISAs and by the commercial RDTs.

Results

The RDTs demonstrated an overall sensitivity of 15.5 %/27.9 %/10.7 % for NS1/IgG/IgA detection in urine samples and 20.4 %/ 34.8 %/11 %/6.2 % for NS1/IgG/IgM/IgA detection in saliva samples. Compared to the in-house NS1 ELISA, the results obtained with the NS1 RDT demonstrated a good correlation with urine samples (kappa coefficient: 0.88) but not with saliva specimens (kappa coefficient: 0.28). RDTs designed for antibody detection in saliva and urine were extremely specific (100 %), but less sensitive than the in-house ELISAs (i.e., reduction of the overall sensitivity by 12.2 % for the RDT designed for IgG detection in urine and by 23.7 % for the RDT detecting anti-DENV IgM in saliva). IgM were not detected in urine, either by RDT or ELISA.

Conclusions

Although the RDTs evaluated here offer an apparently attractive approach for dengue diagnosis, this study suggests that these new commercial kits would require further improvement to increase the sensitivity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1551-x) contains supplementary material, which is available to authorized users.

High prevalence of clinically unsuspected dengue disease among children in Ribeirao Preto city, Brazil

The aim of this study was to analyze the characteristics of Dengue virus (DENV)-infected children and the accuracy of dengue diagnosis based on clinical presentations. The inclusion criteria were children ≥1-year-old presenting febrile illness with 1-7 days of onset. Children (n = 110) aged 2-15 years were included in this study. DENV infection was confirmed with virological tests using serum, salvia, and/or urine samples. The attending pediatricians classified 56/110 (50.91%) of the children as suspected dengue cases. The DENV infection was confirmed by specific laboratory tests in 52/56 (92.9%) of the suspected dengue cases but also in 44/54 (81.5%) of the unsuspected dengue cases; total of 96/110 (87.27%) confirmed dengue cases. The clinical diagnosis gave an overall sensitivity of 54.2% (52/96) and a specificity of 71.4% (10/14). The positive predictive value of the clinical diagnosis was 92.8% and negative predictive value was 18.5%. After the third day of onset of symptoms, the DENV genome detection rate was similar in serum and saliva samples, suggesting that saliva samples represent an alternative to blood samples for early dengue diagnosis. Vaccination against Yellow fever virus did not influence the antibody response against DENV-1, DENV-2, and DENV-3, which circulated during the study period. Although the signs and symptoms were compatible with dengue, the attending pediatricians did not suspect the disease in several children. Therefore, the inclusion of virological tests for early diagnosis in the protocols for dengue surveillance would help in the implementation of prompt treatment of patients and epidemic containment strategies. J. Med. Virol. 88:1711-1719, 2016. © 2016 Wiley Periodicals, Inc.

Infectious Chikungunya Virus in the Saliva of Mice, Monkeys and Humans

Chikungunya virus (CHIKV) is a reemerging, ordinarily mosquito-transmitted, alphavirus that occasionally produces hemorrhagic manifestations, such as nose bleed and bleeding gums, in human patients. Interferon response factor 3 and 7 deficient (IRF3/7^-/-) mice, which are deficient for interferon α/β responses, reliably develop hemorrhagic manifestations after CHIKV infection. Here we show that infectious virus was present in the oral cavity of CHIKV infected IRF3/7^-/- mice, likely due to hemorrhagic lesions in the olfactory epithelium that allow egress of infected blood into the nasal, and subsequently, oral cavities. In addition, IRF3/7^-/- mice were more susceptible to infection with CHIKV via intranasal and oral routes, with IRF3/7^-/- mice also able to transmit virus mouse-to-mouse without an arthropod vector. Cynomolgus macaques often show bleeding gums after CHIKV infection, and analysis of saliva from several infected monkeys also revealed the presence of viral RNA and infectious virus. Furthermore, saliva samples collected from several acute CHIKV patients with hemorrhagic manifestations were found to contain viral RNA and infectious virus. Oral fluids can therefore be infectious during acute CHIKV infections, likely due to hemorrhagic manifestations in the oral/nasal cavities.

Value of Routine Dengue Diagnostic Tests in Urine and Saliva Specimens

Background

Dengue laboratory diagnosis is essentially based on detection of the virus, its components or antibodies directed against the virus in blood samples. Blood, however, may be difficult to draw in some patients, especially in children, and sampling during outbreak investigations or epidemiological studies may face logistical challenges or limited compliance to invasive procedures from subjects. The aim of this study was to assess the possibility of using saliva and urine samples instead of blood for dengue diagnosis.

Methodology/Principal Findings

Serial plasma, urine and saliva samples were collected at several time-points between the day of admission to hospital until three months after the onset of fever in children with confirmed dengue disease. Quantitative RT-PCR, NS1 antigen capture and ELISA serology for anti-DENV antibody (IgG, IgM and IgA) detection were performed in parallel on the three body fluids. RT-PCR and NS1 tests demonstrated an overall sensitivity of 85.4%/63.4%, 41.6%/14.5% and 39%/28.3%, in plasma, urine and saliva specimens, respectively. When urine and saliva samples were collected at the same time-points and tested concurrently, the diagnostic sensitivity of RNA and NS1 detection assays was 69.1% and 34.4%, respectively. IgG/IgA detection assays had an overall sensitivity of 54.4%/37.4%, 38.5%/26.8% and 52.9%/28.6% in plasma, urine and saliva specimens, respectively. IgM were detected in 38.1% and 36% of the plasma and saliva samples but never in urine.

Conclusions

Although the performances of the different diagnostic methods were not as good in saliva and urine as in plasma specimens, the results obtained by qRT-PCR and by anti-DENV antibody ELISA could well justify the use of these two body fluids to detect dengue infection in situations when the collection of blood specimens is not possible.

Dengue is the most important arthropod-borne disease affecting humans and represents a huge public health burden in affected countries. Symptoms are often non-specific hence the need for an early, sensitive and specific diagnosis of dengue for appropriate management as well as for early epidemic detection. Currently, almost all laboratory diagnostic methods require a blood specimen that may be sometimes be difficult or inconvenient to obtain. In this study, we assessed the possibility to use saliva and urine samples as alternatives to blood specimens in dengue diagnosis. We demonstrated that the performances of the different diagnostic methods (RT-PCR, NS1 antigen detection and anti-DENV IgM/IgG/IgA ELISAs) were in general not as good in saliva and urine as in plasma, but that the use of these body fluids obtained by non-invasive methods could be of value in certain circumstances such as outbreak investigations or in young children (once they are old enough to comply to instructions), in addition to the situations when blood cannot be easily collected (e.g., lack of phlebotomist, refusal of the procedure, etc.).

A meta-analysis of the diagnostic accuracy of dengue virus-specific IgA antibody-based tests for detection of dengue infection

Immunoglobulin A (IgA)-based tests have been evaluated in different studies for their utility in diagnosing dengue infections. In most of the studies, the results were inconclusive because of a small sample size. Hence, a meta-analysis involving nine studies with 2096 samples was performed to assess the diagnostic accuracy of IgA-based tests in diagnosing dengue infections. The analysis was conducted using Meta-Disc software. The results revealed that IgA-based tests had an overall sensitivity, specificity, diagnostic odds ratio, and positive and negative likelihood ratios of 73·9%, 95·2%, 66·7, 22·0 and 0·25, respectively. Significant heterogeneity was observed between the studies. The type of test, infection status and day of sample collection influenced the diagnostic accuracy. The IgA-based diagnostic tests showed a greater accuracy when the samples were collected 4 days after onset of symptoms and for secondary infections. The results suggested that IgA-based tests had a moderate level of accuracy and are diagnostic of the disease. However, negative results cannot be used alone for dengue diagnosis. More prospective studies comparing the diagnostic accuracy of combinations of antigen-based tests with either IgA or IgM are needed and might be useful for suggesting the best strategy for dengue diagnosis.

A stacking flow immunoassay for the detection of dengue-specific immunoglobulins in salivary fluid

Paper-based immunoassays, usually in the form of lateral flow tests, are currently the standard platform for home diagnostics. However, conventional lateral tests are often complicated by severe non-specific adsorption of detector particles when applied to test samples containing salivary fluid. It is believed that a high concentration of proteinaceous substances in salivary fluid causes particle aggregation and adhesion. In this study, we developed a stacking flow platform for single-step detection of a target antibody in salivary fluid. Stacking flow circumvents the need for separate sample pre-treatments, such as filtration or centrifugation, which are often required prior to testing saliva samples using paper-based immunoassays. This is achieved by guiding the samples and reagents to the test strip through different paths. By doing so, salivary substances that interfere with the particle-based sensing system are removed before they come into contact with the detection reagents, which greatly reduces the background. In addition, the stacking flow configuration enables uniform flow with a unique flow regulator, which leads to even test lines with good quantification capability, enabling the detection of ~20 ng mL(-1) α-fetoprotein in the serum. We have successfully applied the stacking flow device to detect dengue-specific immunoglobulins that are present in salivary fluid.

Evaluation of the diagnostic accuracy of a new dengue IgA capture assay (Platelia Dengue IgA Capture, Bio-Rad) for dengue infection detection

Considering the short lifetime of IgA antibodies in serum and the key advantages of antibody detection ELISAs in terms of sensitivity and specificity, Bio-Rad has just developed a new ELISA test based on the detection of specific anti-dengue IgA. This study has been carried out to assess the performance of this Platelia Dengue IgA Capture assay for dengue infection detection. A total of 184 well-characterized samples provided by the French Guiana NRC sera collection (Laboratory of Virology, Institut Pasteur in French Guiana) were selected among samples collected between 2002 and 2013 from patients exhibiting a dengue-like syndrome. A first group included 134 sera from confirmed dengue-infected patients, and a second included 50 sera from non-dengue infected patients, all collected between day 3 and day 15 after the onset of fever. Dengue infection diagnoses were all confirmed using reference assays by direct virological identification using RT-PCR or virus culture on acute sera samples or on paired acute-phase sera samples of selected convalescent sera. This study revealed: i) a good overall sensitivity and specificity of the IgA index test, i.e., 93% and 88% respectively, indicating its good correlation to acute dengue diagnosis; and ii) a good concordance with the Panbio IgM capture ELISA. Because of the shorter persistence of dengue virus-specific IgA than IgM, these results underlined the relevance of this new test, which could significantly improve dengue diagnosis accuracy, especially in countries where dengue virus is (hyper-) endemic. It would allow for additional refinement of dengue diagnostic strategy.

Deconstructing "malaria": West Africa as the next front for dengue fever surveillance and control

Presumptive treatment of febrile illness patients for malaria remains the norm in endemic areas of West Africa, and "malaria" remains the top source of health facility outpatient visits in many West African nations. Many other febrile illnesses, including bacterial, viral, and fungal infections, share a similar symptomatology as malaria and are routinely misdiagnosed as such; yet growing evidence suggests that much of the burden of febrile illness is often not attributable to malaria. Dengue fever is one of several viral diseases with symptoms similar to malaria, and the combination of rapid globalization, the long-standing presence of Aedes mosquitoes, case reports from travelers, and recent seroprevalence surveys all implicate West Africa as an emerging front for dengue surveillance and control. This paper integrates recent vector ecology, public health, and clinical medicine literature about dengue in West Africa across community, regional, and global geographic scales. We present a holistic argument for greater attention to dengue fever surveillance in West Africa and renew the call for improving differential diagnosis of febrile illness patients in the region.

Challenges in reducing dengue burden; diagnostics, control measures and vaccines

Dengue is a major public health concern worldwide, with the number of infections increasing globally. The illness imposes the greatest economic and human burden on developing countries that have limited resources to deal with the scale of the problem. No cure for dengue exists; treatment is limited to rehydration therapy, and with vector control strategies proving to be relatively ineffective, a vaccine is an urgent priority. Despite the numerous challenges encountered in the development of a dengue vaccine, several vaccine candidates have shown promise in clinical development and it is believed that a vaccination program would be at least as cost-effective as current vector control programs. The lead candidate vaccine is a tetravalent, live attenuated, recombinant vaccine, which is currently in Phase III clinical trials. Vaccine introduction is a complex process that requires consideration and is discussed here. This review discusses the epidemiology, burden and pathogenesis of dengue, as well as the vaccine candidates currently in clinical development.

Evaluation of efficacy of various immunochromatographic rapid tests for dengue diagnosis

Objective: The immunochromatographic rapid tests facilitate the early diagnosis of dengue by providing evidence of the presence of virus specific proteins (antigens/ antibody) in human blood. Many products for rapid dengue diagnosis are available in the market; the performance of few selected products was evaluated and compared with enzyme linked immuno sorbent assays (ELISA).

Methods: Sera from a large number of patients (n=184) admitted to National Institute of Blood Diseases & Bone Marrow Transplantation (NIBD) were used to determine the efficiency of non-structural (NS) 1, IgA, IgG and IgM based rapid test devices for dengue diagnosis.

Results: The dengue NS1 antigen based device was least efficient while among the antibody based devices the dengue IgA rapid test (RDT) was comparatively better (specificity: 80.95%; sensitivity: 85.21%). This device could detect both primary and secondary dengue infection and was found to be the most sensitive device at all point of sample collection.

Conclusion: The dengue IgA RDT could be a cost effective and efficient rapid test device for timely dengue diagnosis at all levels of healthcare settings.

Diagnostic efficacy of saliva for dengue - a reality in near future? A piloting initiative

BACKGROUND

Dengue, a mosquito-transmitted viral infection presents variable symptoms, including death. Due to their increasing incidences, early detection and improved diagnoses of severe cases are of prime importance. Currently, viral antigens and antibodies are detected by traditional serological tests. However, the introduction of oral fluid as an alternative, has led to many researches. Hence, this prompted us to carry out a pilot study to evaluate the diagnostic efficacy of saliva in detecting dengue antibody by using Enzyme Linked Immunosorbent Assay (ELISA).

AIM AND OBJECTIVES

To evaluate the presence of Dengue antibody in saliva and its sensitivity and specificity through ELISA.

METHODOLOGY AND RESULTS

Twenty seropositive patients and twenty seronegative patients of Dengue were considered individually. Saliva samples collected from these patients were subjected to ELISA test for detection of Dengue antibody. A sensitivity of 100% and a specificity of 100% were obtained for making a diagnosis of Dengue infection.

CONCLUSION

Many studies have been conducted by utilizing saliva as a diagnostic tool, especially in western population. Its advantages over venipuncture are many, especially as it is less invasive, safe, less expensive and as it allows large numbers of samples to be collected easily for screening and epidemiological purposes. In a developing tropical country like India, such a diagnostic tool has to be encouraged. Further research necessitates the implementation of saliva as a diagnostic tool.

Kinetics of dengue non-structural protein 1 antigen and IgM and IgA antibodies in capillary blood samples from confirmed dengue patients

Large-scale epidemiological surveillance of dengue in the field and dengue patient management require simple methods for sample collection, storage, and transportation as well as effective diagnostic tools. We evaluated the kinetics of three biological markers of dengue infection-non-structural protein 1 (NS1) antigen, immunoglobulin M (IgM), and IgA-in sequential capillary blood samples collected from fingertips of confirmed dengue patients. The overall sensitivities and specificities of the tests were 96% and 100%, respectively, for NS1, 58.1% and 100%, respectively, for IgM, and 33% and 100%, respectively, for IgA. During the acute phase of the disease, NS1 was the best marker of dengue infection, with a sensitivity of 98.7%, whereas from day 5, all three markers exhibited relevant levels of sensitivity. This first descriptive study of the kinetics of biological markers of dengue in capillary blood samples confirms the usefulness of this biological compartment for dengue diagnosis and argues for its exploitation in community-level and remote settings.

Dengue specific immunoglobulins M, A, and E in primary and secondary dengue 4 infected Salvadorian children

El Salvador is a Central American country that has been affected by several dengue outbreaks. This study investigated the levels of IgM, IgA, and IgE anti-dengue antibodies in serum samples from children in El Salvador, with a clinical and serological diagnosis of dengue infection during the dengue 4 outbreak in 2002-2003. Seventy one serum samples were tested by ELISA and cases were classified in three groups: 13 primary dengue fever (PDF), 21 secondary dengue fever (SDF), and 37 secondary dengue hemorrhagic fever (SDHF). Also, the specificity of anti-dengue IgM for the different serotypes was tested. No significant differences in the IgM response were found between PDF and SDF, but these were detected between PDF and SDHF (P = 0.0053) and between SDF and SDHF (P = 0.0003). The IgA and IgE values showed a statistically significant difference between primary and secondary groups. The highest positivity percentage of IgA was between 95% (SDF) and 100% (SDHF) towards day 7 of onset of fever. All secondary cases were positive for IgE antibodies. The specificity of IgM was determined for DENV-4 virus in primary and secondary DF groups. This is the first study on dengue cases in Salvadorian children related to the immune response of different immunoglobulins to the type of infection and the clinical picture. Further prospective studies are needed to define if the pattern of immunoglobulins can determine early dengue infection and/or severity.

The Nicaraguan pediatric dengue cohort study: incidence of inapparent and symptomatic dengue virus infections, 2004-2010

Dengue, caused by the four serotypes of dengue virus (DENV), is the most prevalent mosquito-borne viral disease of humans. To examine the incidence and transmission of dengue, the authors performed a prospective community-based cohort study in 5,545 children aged 2–14 years in Managua, Nicaragua, between 2004 and 2010. Children were provided with medical care through study physicians who systematically recorded medical consult data, and yearly blood samples were collected to evaluate DENV infection incidence. The incidence of dengue cases observed was 16.1 cases (range 3.4–43.5) per 1,000 person-years (95% CI: 14.5, 17.8), and a pattern of high dengue case incidence every other year was observed. The incidence of DENV infections was 90.2 infections (range 45.2–105.3) per 1,000 person-years (95% CI: 86.1, 94.5). The majority of DENV infections in young children (<6 years old) were primary (60%) and the majority of infections in older children (≥9 years of age) were secondary (82%), as expected. The incidence rate of second DENV infections (121.3 per 1,000 person-years; 95% CI: 102.7, 143.4) was significantly higher than the incidence rate of primary DENV infections (78.8 per 1,000 person-years; 95% CI: 73.2, 84.9). The rigorous analytic methodology used in this study, including incidence reporting in person-years, allows comparison across studies and across different infectious diseases. This study provides important information for understanding dengue epidemiology and informing dengue vaccine policy.

Dengue is a major public health problem worldwide with 40 million cases annually. We conducted a large-scale prospective cohort study of dengue virus infection in children aged 2–14 years in Managua, Nicaragua. The observed rate of dengue cases was 16.1 cases per 1,000 persons per year. The observed rate of dengue virus infections was 90.2 infections per 1,000 persons per year. The observed rate of dengue virus infections is similar to the rates reported in Asian cohort studies, while the rate of dengue cases was lower than that observed in Asian cohort studies. The rate of dengue cases varied more than the rate of dengue virus infections, and a clear pattern of high dengue case incidence every other year was observed. The rigorous analytic methodology used in this study allows comparison of incidence of dengue virus infections and dengue cases across studies and across different infectious diseases. Our estimates of the burden of dengue in Nicaraguan children have significant policy implications for dengue vaccines as they become available.

Evaluation of the diagnostic utility of the traditional and revised WHO dengue case definitions

Dengue, a mosquito-borne viral illness, is a major public health problem worldwide, and its incidence continues to increase. In 2009, the World Health Organization published guidelines that included a revision of the dengue case definition. Compared to the traditional definition, the revised case definition relies more on signs than on symptoms, making it more applicable to young children. We evaluated the diagnostic utility of both case definitions in two studies of pediatric dengue in Managua, Nicaragua. In a community-based cohort study, we included data from 3,407 suspected dengue cases, of which 476 were laboratory-confirmed. In the second study, we collected information from 1,160 participants recruited at the national pediatric reference hospital (723 laboratory-confirmed). In the cohort study, the traditional definition had 89.3% sensitivity and 43.1% specificity, while the revised definition yielded similar sensitivity (86.6%) and higher specificity (55.2%, p<0.001). In the hospital study, the traditional case definition yielded 96.7% sensitivity and 22.0% specificity, whereas the revised case definition had higher sensitivity (99.3%, p<0.001) but lower specificity (8.5%, p<0.001). We then evaluated the performance of two diagnostic models based on the signs/symptoms included in each definition by analyzing the effect of increasing numbers of signs/symptoms on the sensitivity and specificity of case capture. Receiver operating characteristic analysis showed a slightly better performance for the revised model in both studies. Interestingly, despite containing less symptoms that cannot be readily expressed by children aged less than 4 years, the revised definition did not perform better in this age group. Overall, our results indicate that both case definitions have similar capacity to diagnose dengue. Owing to their high sensitivity and low specificity, they should be primarily used for screening purposes. However, in a primary care setting, neither of the case definitions performed well as a screening test in younger children.

Dengue, a mosquito-borne viral infectious disease, is a major health problem worldwide. Its incidence has dramatically increased in the last 3 decades, particularly in the Americas. The traditional World Health Organization dengue case definition was in use for over 30 years, but in 2009 a revised dengue case definition, containing fewer symptoms and more signs, was published. In this study, we evaluate the diagnostic utility of both case definitions in children in Managua, Nicaragua. We used clinical data from suspected dengue cases enrolled at two different sites: a health center and the national pediatric reference hospital. Laboratory tests were performed to determine dengue virus infection status. At both sites, the case definitions showed high sensitivity (≥85%) and low specificity (8–55%). In children under 4 years old, who cannot express some of the symptoms included in the definitions, both case definitions showed reduced sensitivity and increased specificity. This reduction was particularly important in the health center, where sensitivity dropped below 50%. In conclusion, both case definitions should be primarily used for screening and not for diagnosis, and caution must be exercised when applying the definitions to younger children. This is the first published evaluation of the revised dengue case definition in pediatric populations.

Symptomatic versus inapparent outcome in repeat dengue virus infections is influenced by the time interval between infections and study year

Four dengue virus serotypes (DENV1-4) circulate globally, causing more human illness than any other arthropod-borne virus. Dengue can present as a range of clinical manifestations from undifferentiated fever to Dengue Fever to severe, life-threatening syndromes. However, most DENV infections are inapparent. Yet, little is known about determinants of inapparent versus symptomatic DENV infection outcome. Here, we analyzed over 2,000 DENV infections from 2004 to 2011 in a prospective pediatric cohort study in Managua, Nicaragua. Symptomatic cases were captured at the study health center, and paired healthy annual samples were examined on a yearly basis using serological methods to identify inapparent DENV infections. Overall, inapparent and symptomatic DENV infections were equally distributed by sex. The mean age of infection was 1.2 years higher for symptomatic DENV infections as compared to inapparent infections. Although inapparent versus symptomatic outcome did not differ by infection number (first, second or third/post-second DENV infections), substantial variation in the proportion of symptomatic DENV infections among all DENV infections was observed across study years. In participants with repeat DENV infections, the time interval between a first inapparent DENV infection and a second inapparent infection was significantly shorter than the interval between a first inapparent and a second symptomatic infection. This difference was not observed in subsequent infections. This result was confirmed using two different serological techniques that measure total anti-DENV antibodies and serotype-specific neutralizing antibodies, respectively. Taken together, these findings show that, in this study, age, study year and time interval between consecutive DENV infections influence inapparent versus symptomatic infection outcome, while sex and infection number had no significant effect. Moreover, these results suggest that the window of cross-protection induced by a first infection with DENV against a second symptomatic infection is approximately 2 years. These findings are important for modeling dengue epidemics and development of vaccines.

The four serotypes of the mosquito-borne dengue virus (DENV) infect an estimated 100 million humans annually, resulting in tens of millions of dengue cases and hundreds of thousands of cases of severe disease. However, infection with DENV does not always lead to clinical signs, and a large proportion of DENV infections are inapparent. Here, we studied the factors that influence whether a DENV infection is inapparent or symptomatic. Data from over 2,000 DENV infections (∼1,600 inapparent and ∼400 symptomatic) were collected during 7 years from an ongoing prospective cohort study of children in Managua, Nicaragua. We show that whether a person is infected for the first, the second, or the third time with different DENV serotypes, the proportion of symptomatic infections is similar. However, the proportion of symptomatic infection varied substantially across study years, and symptomatic infections tended to happen in older children when compared to inapparent infections. We also show that if a second DENV infection happens within a period of ∼2 years after the first infection, the second infection is more likely to be inapparent. However, if the time interval between first and second DENV infections is longer, this protection wanes and the infection is likely to be symptomatic. These findings are important for the modeling of dengue epidemics and the development of new vaccines.

Correlation between dengue-specific neutralizing antibodies and serum avidity in primary and secondary dengue virus 3 natural infections in humans

Although heterotypic secondary infection with dengue virus (DENV) is associated with severe disease, the majority of secondary infections are mild or asymptomatic. The mechanisms of antibody-mediated protection are poorly understood. In 2010, 108 DENV3-positive cases were enrolled in a pediatric hospital-based study in Managua, Nicaragua, with 61 primary and 47 secondary infections. We analyzed DENV-specific neutralization titers (NT₅₀), IgM and IgG avidity, and antibody titer in serum samples collected during acute and convalescent phases and 3, 6, and 18 months post-infection. NT₅₀ titers peaked at convalescence and decreased thereafter. IgG avidity to DENV3 significantly increased between convalescent and 3-month time-points in primary DENV infections and between the acute and convalescent phase in secondary DENV infections. While avidity to DENV2, a likely previous infecting serotype, was initially higher than avidity to DENV3 in secondary DENV infections, the opposite relation was observed 3–18 months post-infection. We found significant correlations between IgM avidity and NT₅₀ in acute primary cases and between IgG avidity and NT₅₀ in secondary DENV infections. In summary, our findings indicate that IgM antibodies likely play a role in early control of DENV infections. IgG serum avidity to DENV, analyzed for the first time in longitudinal samples, switches from targeting mainly cross-reactive serotype(s) to the current infecting serotype over time. Finally, serum avidity correlates with neutralization capacity.

Dengue is the most common mosquito-borne viral illness in humans, with 3 billion people at risk for infection. Four different dengue virus serotypes (DENV1–4) cause the disease, which can be either inapparent or present with flu-like symptoms (Dengue Fever, aka “breakbone fever”). The disease can be more severe and sometimes fatal, with signs of bleeding and vascular leakage leading to shock (Dengue Hemorrhagic Fever/Dengue Shock Syndrome). No specific treatment or vaccine is available. Understanding how the human immune response develops during a natural infection can be beneficial for future vaccine studies and trials. DENV-specific serum neutralizing capacity may play a role in protection. The neutralization capacity of the serum may depend on the serum avidity against DENV, the amount (or titer) of the anti-DENV antibodies, and the accessibility of the epitopes targeted by these antibodies. Here we show that DENV-specific IgM antibodies likely play a role in neutralization during primary DENV infections and show a correlation between serum avidity and neutralization capacity in secondary DENV infections, with greater avidity to a previously infecting DENV serotype as compared to the current infecting DENV serotype in the early phases of infection, switching over time to the opposite situation.

An evaluation of dried blood spots and oral swabs as alternative specimens for the diagnosis of dengue and screening for past dengue virus exposure

Non-invasive specimens for dengue diagnosis may be preferable where venous blood is difficult to collect and/or process, such as community-based or remote settings or when sampling from young children. We evaluated the performance of oral swabs and dried blood spots (DBS), compared with plasma, in diagnosing acute dengue and screening for past dengue virus (DENV) exposure. DENV-specific immunoglobulin (Ig) M, IgG, and NS1 antigen were detected both in oral swabs and DBS from acute patients. Oral swabs were less sensitive (IgM: 68.7%, IgG: 91.9%, NS1: 64.7%), but retained good specificity (100%, 92.3%, 95.8%, respectively) compared with plasma. DBS displayed high sensitivity (IgM: 100%, IgG: 96%, NS1: 100%) and specificity (IgM: 75%, IgG: 93%). DENV RNA was amplified from DBS (sensitivity 95.6%) but not from oral swabs. DENV-IgG (indicative of past flavivirus exposure) were detected with moderate sensitivity (61.1%) but poor specificity (50%) in oral swabs from healthy volunteers. Dried blood spots allow sensitive and specific diagnosis of acute dengue by serological, molecular, and antigen detection methods. Oral swabs may be an adequate alternative where blood cannot be collected.

Genome-wide patterns of intrahuman dengue virus diversity reveal associations with viral phylogenetic clade and interhost diversity

Analogous to observations in RNA viruses such as human immunodeficiency virus, genetic variation associated with intrahost dengue virus (DENV) populations has been postulated to influence viral fitness and disease pathogenesis. Previous attempts to investigate intrahost genetic variation in DENV characterized only a few viral genes or a limited number of full-length genomes. We developed a whole-genome amplification approach coupled with deep sequencing to capture intrahost diversity across the entire coding region of DENV-2. Using this approach, we sequenced DENV-2 genomes from the serum of 22 Nicaraguan individuals with secondary DENV infection and captured ∼75% of the DENV genome in each sample (range, 40 to 98%). We identified and quantified variants using a highly sensitive and specific method and determined that the extent of diversity was considerably lower than previous estimates. Significant differences in intrahost diversity were detected between genes and also between antigenically distinct domains of the Envelope gene. Interestingly, a strong association was discerned between the extent of intrahost diversity in a few genes and viral clade identity. Additionally, the abundance of viral variants within a host, as well as the impact of viral mutations on amino acid encoding and predicted protein function, determined whether intrahost variants were observed at the interhost level in circulating Nicaraguan DENV-2 populations, strongly suggestive of purifying selection across transmission events. Our data illustrate the value of high-coverage genome-wide analysis of intrahost diversity for high-resolution mapping of the relationship between intrahost diversity and clinical, epidemiological, and virological parameters of viral infection.